1. Field of the Invention
This invention relates to an ignition system for an internal combustion engine, and more particularly, an ignition system of the condensor-discharge type for an internal combustion engine, which ignition system does not use a signal coil for determining the ignition position.
2. Description of the Prior Art
An ignition system of the condensor-discharge type for an internal combustion engine which has been conventionally used in the art is constructed in such a manner that condensor is charged by means of the half wave output having positive polarity from an exciter coil provided in a magneto and a discharge control thyristor is turned on when a turn-on signal or gate signal is provided utilizing the half wave output having negative polarity generated from the exciter coil subsequent to the half wave output, so that the condensor may be discharged through the thyristor to the primary winding of an ignition coil to carry out the ignition operation.
Such a conventional ignition system of the condensor-discharge type has an advantage of rendering the structure of a magneto to be installed in an engine simple because it can eliminate the provision of a signal coil required to determine the ignition position. However, in the conventional ignition system, an electric current flows from the exciter coil to the condensor during the positive half wave output of the exciter coil to cause an armature reaction to appear in the exciter coil, so that the rising of a wave form of the negative half wave output generated from the exciter coil subsequent thereto is delayed resulting in the ignition position of an engine being delayed. Such defect is substantially increased with the increase in engine speed (rpm), to thereby cause the relationship between the ignition position .theta..sub.i and the engine speed N in the conventional ignition system of such type to be as shown in FIG. 5. Thus, it will be noted that the conventional ignition system has a disadvantage that the ignition position is substantially delayed at a high engine speed. In FIG. 5, the axis of ordinates designates an angle of the ignition position of an engine, supposing that an angle of the ignition position at the normal engine speed of 3000 rpm based on the top dead point of the engine is defined to be 0 degree.
Also, in the conventional ignition system of such type, the ignition operation is carried out also during the reverse rotation of the two-cycle engine, because a turn-on signal is supplied to the thyristor to discharge the condensor also when the engine is reversely rotated; thus, it is not suitable for use as an ignition system for a two-cycle engine.